be a thorn in (someone's) side
To be a constant or persistent cause of annoyance, frustration, or trouble. My professor was an environmental activist when he was younger, and, apparently, he was quite a thorn in the oil companies' sides at the time.
crown of thorns
Something that causes one pain and suffering. Alludes to the crown of thorns that Jesus was made to wear before his crucifixion. Its usage is similar to the phrase "cross to bear." I can't stand to see how sick she has become. This illness is a real crown of thorns. This class is my crown of thorns. No matter how much I study, I just keep getting awful grades.
thorn in (someone's) side
A constant or persistent cause of annoyance, frustration, or trouble. My professor was an environmental activist when he was younger, and, apparently, he was quite a thorn in the oil companies' sides at the time. My little brother is such a thorn in my side—he always wants to do stuff with me, especially when I'm trying to hang out with my friends.
thorn in the flesh
A constant or persistent cause of annoyance, frustration, or trouble. My little brother is such a thorn in the flesh—he always wants to do stuff with me, especially when I'm trying to hang out with my friends.
thorn in (one's) side
A person or thing that is frequently problematic and/or annoying. My new neighbors blast music at all hours of the day and night—they're a real thorn in my side My car has become such a thorn in my side—today is the third day this week that it wouldn't start!